fix ppl test errors (#10036)

python/llm/dev/benchmark/perplexity/README.md

@@ -3,9 +3,9 @@ Perplexity (PPL) is one of the most common metrics for evaluating language model
 
 ## HOW TO RUN
 ```python
-python run.py --model_path <path/to/model> --low_bit sym_int4 fp4 mixed_fp4 sym_int8 fp8_e5m2 fp8_e4m3 mixed_fp8 --device xpu --dataset path=<dataset_path>,name=<dataset_name>
+python run.py --model_path <path/to/model> --precisions sym_int4 fp4 mixed_fp4 sym_int8 fp8_e5m2 fp8_e4m3 mixed_fp8 --device xpu --dataset path=<dataset_path>,name=<dataset_name>
 ```
 A more specific example to run perplexity on Llama2-7B and wikitext:
 ```python
-python run.py --model_path meta-llama/Llama-2-7b-chat-hf --low_bit float16 sym_int4 --device xpu --dataset path=wikitext,name=wikitext-2-raw-v1
+python run.py --model_path meta-llama/Llama-2-7b-chat-hf --precisions float16 sym_int4 --device xpu --dataset path=wikitext,name=wikitext-2-raw-v1
 ```

python/llm/dev/benchmark/perplexity/ppl.py

@@ -19,6 +19,7 @@ import numpy as np
 import torch
 from tqdm import tqdm
 from transformers import AutoTokenizer
+import gc
 
 from bigdl.llm.transformers import AutoModelForCausalLM
 
@@ -81,4 +82,9 @@ class BigDLPPL:
                 self.ppl_evaluator(data.numpy()[0, seq_len//2:, :], input_ids_chunks.numpy()[0, seq_len//2:])
             progress_bar.set_description(f"{self.ppl_evaluator}")
 
+        torch.xpu.synchronize()
+        torch.xpu.empty_cache()
+        del self.model
+        gc.collect()
+        
         return self.ppl_evaluator.result()

python/llm/dev/benchmark/perplexity/run.py

@@ -44,7 +44,7 @@ def main():
     additional_model_kwargs = parse_kwargs(args.model_kwargs)
     summary = {}
     for precision in args.precisions:
-        model_kwargs = additional_model_kwargs
+        model_kwargs = additional_model_kwargs.copy()
         if precision in ggml_tensor_qtype.keys():
             model_kwargs['load_in_low_bit'] = precision
         else: